The present invention relates to a method of producing powder from a sticky, tacky, adhesive or viscous thin-film.
Polymer compounds are substances used frequently in a wide variety of uses but many of them show their stickiness by being heated thus making their conversion into powders difficult. For example, when a substance showing its stickiness at a high temperature is used to produce a powdery product by a spray drying method as one of ordinarily drying methods, there is the problem of attaching (or adhesion) of the sticky substance onto an inside of a spray drying tower thereof, thus making it difficult to produce the powdery product therefrom. To solve this problem, for example, in the case that a polycarboxylic acid copolymer as the substance showing is stickiness at a high temperature is powdered, JP-B 2669761 discloses a method of spray-drying a liquid polycarboxylic acid copolymer and an inorganic powder such as a cement material in order to obtain powder. In this production of powder by such spray drying method, however, it become essential to incorporate a non-sticky substance such as an inorganic powder. Therefore, in order to improve a yield (or recovery ratio) thereof, it become necessary to incorporate a large amount of the non-sticky substance. Variety on a composition thereof is thus limited. Further, this method as a prior art has the problem that when the incorporated amount of the inorganic powder is reduced, the yield of the powder is lowered. With respect to a polymer compound which in a thin-film form does not show its stickiness, there is known a method of drying and powdering a thin-film formed from a solution of the said polymer compound. However this method is limited for the material of which a thin-film by drying becomes flaky actually.
The object of the present invention is to provide a method of producing powder at a high yield from a sticky thin-film with high variety on a composition thereof without necessitating an incorporation of a non-sticky substance.
The present invention relates to a method of producing powder, which comprises forming a sticky thin-film on a support, reducing a stickiness (tackiness, adhesiveness or viscousness) of the said thin-film and powdering the said thin-film.
The stickiness of the thin-film can be reduced by cooling the thin-film. After stripping (peeling or releasing) the thin-film from the support, a gas stream may be fed (or supplied) to a surface of the thin-film. The thin-film on the support may be heated.
It is preferable that the sticky thin-film contains a polymer compound.
The powder obtained by the method of the present invention can be used as a cement dispersant. The present invention also provides use thereof, a method of dispersing cement and a cement composition comprising the said powder.
The method of the present invention may further comprise a step of processing (or treating) the thin-film by running the thin-film on a surface of a cylinder and pressure-sensitively adhering (or contact-bonding) the thin-film onto the surface of the cylinder by means of an auxiliary roll which changes a size of a clearance (gap or distance) between itself and the cylinder depending on a change in a thickness of the said thin-film. The cylinder may have been heated or cooled. In this manner, the stickiness of the thin-film can regulate and average the thickness thereof.
In the present invention, the xe2x80x9csticky thin-filmxe2x80x9d is a thin-film having an attaching (adherent or bonding) property even upon application of a slight pressure in a short time. For example, it has a characteristic to adhere onto an another thin-film or the other material (e.g. a constituent member in a device or instrument used in the producing process) if the said thin-film is stripped from the support. The stickiness includes one being exhibited by heating.
The stickiness of the thin-film can be confirmed by, for example, the following manner. If, when parts in the thin-film or the thin-films stripped from a support(s) are brought into contact with each other, both of the parts or thin-films adhere each other, the thin-film is called the sticky thin-film. Alternatively, if, when a thin-film stripped from a support is brought into contact with a member on which the thin-film may be brought into contact during the production, both of the thin-film and the member adhere each other, the thin-film is called the sticky one. In the latter case, if, when the member onto which the thin-film adheres is turned upside down (or turned about), the thin-film does not drop by gravity from the member, the thin-film is judged to be sticky. Because the object toward which the thin-film shows its stickiness is varied depending on a type of the sticky thin-film, it is also preferable that the device or instrument used in the producing process is composed of materials toward which the thin-film does not show the stickiness.